1. Field of the Invention
The invention relates generally to radio systems and more particularly to an exchangeable antenna attenuator pad for a radio system. The radio system includes a hub transceiver and a plurality of customer premise transceivers at different distances from the hub transceiver, each of the customer premise transceivers including an antenna having the exchangeable attenuator pad mounted thereon.
2. Description of the Prior Art
A common type of radio system includes a hub transceiver in radio signal communication with several customer premise transceivers at different distances from the hub. The different distances cause a problem, sometimes called the near-far problem, where the signal strength of the radio signal received from a nearby transceiver is greater, sometimes much greater, than the signal strength of the radio signal received from a faraway transceiver. When the signal strengths vary too greatly the transceivers will not have enough dynamic range to receive the largest signals with minimal distortion while discerning the smallest signals from noise. In order to obtain a good signal-to-noise ratio for the low signal strength radio signals, the receiver in the transceiver must be calibrated so that the maximum received signal strength matches the maximum signal strength for proper operation within the receiver.
Existing radio systems use one of several alternative calibration schemes for attempting to resolve the near-far problem. However, all the alternative schemes have limitations of one kind or another. In one alternative, a variable attenuator is provided at the hub transceiver. The variable attenuator is controlled for providing a different attenuation for communication with each customer premise transceiver. However, such variable attenuator is not often used where the hub transceiver does not have foreknowledge of which of the customer premise transceivers will be next received because the early part of the radio signal for the next customer premise transceiver may be lost before the attenuator can be set to the proper variation.
Other existing radio systems resolve the near-far problem with a variable attenuator at the customer premise transceiver. Typically, the variable attenuator is included in the design of the radio frequency (RF) section of the transceiver very soon or immediately after the antenna in order to prevent overloading the front end of the receiver. The variable antenna may be set to the appropriate attenuation at the customer site during the installation. Unfortunately, such variable attenuator is expensive and the commercial acceptance of the customer premise transceiver is very sensitive to cost. Alternatively, because any one customer premise transceiver is at a fixed distance to the hub transceiver the variable attenuator in the RF section could be replaced by a fixed attenuator pad that is factory-selected for each particular customer premise transceiver. Such fixed attenuator is typically much less expensive than a variable attenuator. However, the factory process of customizing each customer premise transceiver increases the complexity of the order processing, manufacture, inventory, and shipment of the transceiver, thereby increasing its cost. It would be less expensive to install the fixed attenuator in the field at the customer site. However, the RF section and in many cases the entire radio is built onto the antenna as a sealed unit and it is undesirable to open the unit at the site. Conceivably, this problem could be solved where an RF preamplifier built onto the antenna connects with a coaxial cable to the remaining portion of the radio by placing a coaxial attenuator in the cable. However, this is usually not practical because it is usually desirable to power the preamplifier through the coaxial cable.
There is a need for an inexpensive solution to the near-far problem for a radio system having several customer premise transceivers at varying distances from a hub transceiver.
It is therefore an object of the present invention to provide an exchangeable attenuator pad for mounting to the outside of an antenna in the path of a radio signal radiated by the antenna.
Another object is to provide a radio system having a hub transceiver and a plurality of customer premise transceivers having different transmission path losses between the respective customer premise transceivers and the hub transceiver where each of the customer premise transceivers includes an antenna having a selected exchangeable attenuator pad mounted thereon for compensating for the different transmission path losses and providing predetermined incoming signal strengths at each of the customer premise transceivers and at the hub transceiver.
Briefly, a preferred embodiment of the present invention includes a radio system having a hub transceiver and several remote customer premise transceivers where each customer premise transceiver is in two way communication with the hub transceiver. The customer premise transceiver includes an antenna having an exchangeable attenuator pad of the present invention mounted on the antenna in the path of the airwave signal for attenuating the signal that is transmitted or received with the antenna. The attenuator pad is selected from a set of attenuator pads having differing attenuations. A high level of attenuation is selected where the customer premise transceiver is relatively near to the hub transceiver. A lower level or no attenuation is selected where the customer premise transceiver is relatively far from the hub transceiver.
An advantage of the exchangeable attenuator pad of the present invention is that a radio signal radiated by an antenna is inexpensively and conveniently attenuated by a selectable attenuation without requiring an internal change to a transceiver.
An advantage of the radio system of the present invention is that selected exchangeable attenuator pads selectably attenuate signals for providing predetermined incoming signal strengths at each of the transceivers in the radio system in spite of the different transmission path losses between the transceivers without requiring internal changes to any of the transceivers.